The present invention is directed to control devices for bicycles and, more particularly, to a motor driven shifting device for shifting a bicycle transmission.
There are two major types of bicycle transmissions currently marketed. One type of bicycle transmission uses a derailleur to shift a chain from one sprocket to another to change the drive ratio, and the other type uses a planetary gear mechanism disposed inside a rotating hub such as a wheel hub to change the drive ratio. In either case, an operating member such as a lever, push rod or rotatable ring is moved to operate the transmission, and the operating member is connected to a transmission actuating member such as a control wire or link that is pulled or released by the rider to cause the desired movement of the operating member. To facilitate the operation of the transmission in a pull and release manner, a return spring commonly is used to bias the operating member to an initial state. The transmission then is operated by moving the operating member against the progressively increasing force of the return spring and the natural resistance by the transmission to changing gears.
Motor driven bicycle transmissions are becoming more common. Such motor driven bicycle transmissions relieve the rider of the task of manually pulling and releasing the transmission actuating member. A typical motor driven bicycle derailleur transmission is disclosed in U.S. Pat. No. 4,490,127. In that patent a motor is connected to a wire winding member through a gear reduction mechanism for pulling and releasing a control wire coupled to the derailleur. The motor usually is mounted to the frame somewhat remote from the bicycle transmission to accommodate the length of control wire. When a motor drive unit is used with a hub transmission of the type that is controlled by an actuating rod slidably disposed in the hub axle, then the control wire must be connected to a bell crank mechanism or some other lever mechanism that moves the actuating rod. The size and shape of the bell crank mechanism and the actuating rod are not always known in advance, so the installer must mount the bell crank mechanism to the bicycle, mount the motor to the bicycle, determine the optimum length of control wire to use with the system, and connect the entire system together. Thus, mounting such a motor driven system can be very complicated. If there is some incompatibility between the bell crank mechanism and the hub transmission, such as that which occurs when the actuating rod is too short or too long for the available bell crank mechanism, or if there is some incompatibility between the bell crank mechanism and the motor drive unit, then the installer must somehow adapt the incompatible part. This can be very difficult if not impossible to accomplish.